So basically you're abusing the system, by constantly spamming farming runs, well, which are not exactly farming runs, to take advantage of gaining extra flags, which in my opinion is an unfair advantage to those that are not abusing the system.
Therefore there is no point in having a plunderer of the day award, if someone, or probably in your case, a group of co-players, are sitting there all day and spamming the barbs with minimum troops.
If that is the case and it would appear so, then TW might as well scrap the award of a flag for the plunderer of the day, or adjust the system, where a player or players can't send 1000's of attacks to the same Barbarian village, as it is pointless for other players to try and obtain this award..